When a bacterium (Bacillus megaterium) produces a spore, it passes through a process of differentiation in which one cell (destined to become a spore) develops within another (the sporangium). These two cells differ markedly in morphology and physiology. This research aims at determining whether the membranes of these two cellular compartments differ in structure or composition, and if so, whether the developing cell is able to simultaneously produce two types of membranes, spatially and functionally distinct. One of the principal tools we are using in exploring differences in the surfaces of the sporangial and forespore membrane is a bacteriocin which kills sensitive cells after binding to a specific receptor in the cell surface. We have purified the bacteriocin and propose to carry out studies on its chemical composition and its interaction with the cell membrane.